Challenges in Tennis: How Do They Work?

Technology in tennis has revolutionised the game in the past couple of decades. Advancements in racket, string and footwear technology has taken the game to new heights, with modern players hitting the ball a lot harder and being much more athletic than generations before them.

However, automated line calling systems like Hawkeye have also transformed professional tennis and brought a lot more data to the game. This helps players not only rely on more accurate line calling, but also gives them insights into their shot statistics.

So, let’s take a closer look at what challenges are, how they work and the different line call challenging systems out there today.

What is a Challenge in Tennis? 

Challenges in tennis are made possible thanks to the advanced camera and ball tracking technology installed at professional tennis tournaments. 

A challenge works by a player questioning a line call and then asking the umpire to refer to the built-in ball tracking system to review the ball. 

This usually occurs when a player believes a shot of theirs has landed inside the court, but a line umpire has called it out. 

In this instance, the player will call out ‘challenge’ and the chair umpire will call up to the ball tracking system review box and ask them to review their footage of the ball, to see if it landed in or out. 

Challenges not only provide players with the opportunity to question a line call they think may be incorrect, but they also bring an added element of drama and excitement to the sport for crowds to enjoy. 

Drama is something that can occur within a challenge itself, as in the early days players were not used to the system. Oftentimes, a challenge itself would be questioned, when a player disagreed with the system on particularly close calls. There have been many instances of professional players losing it over a line call that they clearly thought was out, even claiming to see a mark proving this, despite the challenge system saying the ball caught a slither of the line. 

There have even been times when a player has asked for a call to be challenged, but the system has been unavailable, giving an unfair advantage to their opponent. 

Now, let’s take a closer look at the history of challenges and the different systems used to produce them.

When Were Challenges Introduced?

The challenge system was first introduced into professional tennis in March 2006, when Hawkeye rolled out its innovation at the NASDAQ-100 Open in Florida.

Over the following couple of years, challenges were introduced at the grand slams and other major tournaments like Masters 1000 events. 

However, in the early days challenges caused some controversy as the rudimentary systems operated with a degree of error. This caused some instances when a ball would be called in, but instant video replay would show the ball clearly being out. 

This would leave both the players and the umpire in a difficult position, often ending in one player feeling hard done by. 

Nowadays, challenges are commonplace at most top-tier professional tournaments, particularly on show courts. This offers more consistency to the players and reduces the level of human error in the sport.

How Many Challenges Do You Get? 

Players typically get three challenges per set in a tennis match. Players also receive one additional challenge if the set goes into a tiebreak. 

If a player challenges a call and gets it right, then they retain all of their existing challenges. However, if they challenge a call and they are incorrect, they lose one of their challenges. 

If a player runs out of challenges, they can no longer question any line calls until a new set has begun.

How Challenges Work

If a player decides to challenge a line call, they must do so in a timely and clear manner. This means that a player cannot run over to look at a mark, ponder their decision for a few seconds and then decide to challenge. Instead, challenges should be done pretty much immediately after the call is made that a player wants to dispute. 

Players tend to call out ‘challenge’ and raise up their arm or racket to signal to the chair umpire that they want to dispute a call made by a line judge. 

The chair umpire has the authority to dismiss a challenge if it is not made clearly or in a timely manner. As you can imagine, this can cause some arguments in court. 

There are a few major players in the automated line-calling industry. These include Cyclops and Hawkeye, although some smaller companies like In/Out and Playsight have made their way into recreational tennis clubs.


One of the first systems to be introduced for the purposes of automated line calls was Cyclops. In the early 2000s, Cyclops would use suspended infrared lasers to automatically determine whether the ball had landed inside the service box or not. 

Whilst Cyclops was definitely a huge innovation in the tennis world, it was limited to just main service line calls (not center or sidelines) and was only really available for use on stadium courts.


Hawkeye was also introduced in the early 2000s and has become the dominant force in automated line calls. The system had already been used in cricket prior to its use in tennis and is also currently deployed in Soccer, Snooker, Gaelic games, Australian Football, and Badminton. 

The system uses advanced video camera technology to produce a map of the court and accurately track whether a ball has bounced in or out of the court dimensions. Hawkeye has been refined over the years and is said to work with a 95% degree of accuracy. 

There have been criticisms of Hawkeye over the years due to disputes over its accuracy, use only on high-profile televised courts, and the time taken for a call to be made. 

However, it looks like Hawkeye is here to stay despite its critics. The system has been rolled out across hundreds of tournaments worldwide and has proved to be one of the biggest steps forward in technological innovation in professional tennis to date.

Automated Line Calls

Products like Hawkeye Live offer automated line calls, which effectively remove the need for traditional human line judges. The idea here is that human error can be taken out of the game, and this has been introduced into both the ATP and WTA tours in recent years. 

In fact, the ATP announced recently that it aims to phase out human line judges and only use automated line calls at the start of the 2025 season.

Challenges in Tennis: Help or Hindrance?

Overall, challenges offer a form of entertainment to crowds, as well as an opportunity for professional tennis players to overrule human error in line calls. The use of systems like Hawkeye and Cyclops has revolutionized the sport and made it a lot more popular for TV viewing. 

Challenges and automated line calls have given professional tennis players the opportunity to benefit from more accurate line calls, which is especially important given the amount of money, prestige, and ranking points on the line in the modern game. 

This certainly leads to fewer disputes overall between tennis players and line judges, but challenges do also create controversies of their own. 

However, they have overall been a net positive for the game and are clearly only becoming more popular in tennis due to the adoption of automated line calls. 

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